A time of magnetic flux

My latest Mind and Matter column in the Wall Street Journal is about the weakening of the magnetic field and, more generally, the question of how we scare ourselves by knowing more:

The earth's magnetic field is weakening at an accelerating rate. It is 15% weaker than it was at the time the north magnetic pole was "discovered"-and claimed for King William IV-by a British explorer in 1831. Should we be worried?

What's more, the north magnetic pole, after meandering through Canadian islands for half a millennium, is heading off across the Arctic Ocean toward Russia at the breakneck speed of 37 miles a year. It will pass close to the geographical North Pole in a few years. With the dastardly Russians about to pinch this British heirloom, should we be doubly worried?

I am, of course, just showing how easy it is to make something seem scary by failing to put it in context. The weakening of the magnetic field is indeed "unprecedented since records began," but records began very recently. Geological evidence suggests that this fluctuation is well within normal bounds: The magnetic field was much weaker 20,000 years ago.

Some of the scares we take more seriously are similarly torn from context. Four years ago (though not more recently), the retreat of Arctic sea ice was unprecedented since records began, but records began only in 1979, and there is lots of evidence of greater ice retreats in past periods, such as the 1930s or 7,000 years ago. Recent floods in Brisbane, Australia, were the worst...since 1974. And so on. Always ask: Since when?

As for the movement of the magnetic pole, the sudden acceleration is interesting and mysterious, but there is no evidence that it's dangerous. Since we cannot really measure the flows of fluid in the outer core of the earth, we cannot predict the shape of the dynamo that generates the field. Something seems to be going on deep beneath the New Siberian Islands that is drawing the pole toward them.

Though odds are strongly against it, it is just possible that this is the beginning of a polar reversal, when the North and South magnetic poles swap places. This used to happen quite often-by which I mean every hundred thousand years or so-but it's now 780,000 years since it last occurred, an unusually long interval.

During such a reversal there is probably a very brief interval (oops, there I go again; by "very brief" I mean a thousand years or so) when the earth has no stable magnetic field. This does not seem to have bothered our ancestors: There is no evidence of biological extinctions peaking during magnetic-pole reversals.

But maybe they affected bird migration. Birds generally use the sun, stars, and local landmarks for navigation, but they appear to be able to tap into magnetic lines of force as a backup system. So in a reversal, more birds may go missing.

Perhaps the next magnetic reversal will play havoc with communications by dropping the magnetic shield that protects our electronics from solar storms and cosmic rays. Our computers will crash for a thousand years. Help. Let's form a U.N. agency!

By living in a time when science finds things out, we too easily scare ourselves. Asteroid impacts did not keep our ancestors awake at night because they did not know that asteroids existed, let alone that one wiped out the dinosaurs. Two centuries ago, nobody knew of ice ages, so we imagined a stable climate. Two decades ago, before we drilled an ice core in Greenland, nobody knew of the abrupt climate lurches that happened at the end of the last ice age. Two years ago, no tourist knew that tiger sharks frequented Red Sea beach resorts.

Context is all. Most of the scary things we discover about our planet are infrequent and improbable, or getting a lot less scary because of human ingenuity. Stop fretting.

Update: a reader challenges me about sea ice in the 1930s. The retreat of Nordic Seas ice (part of the Arctic) was indeed greater then than now, according to recent research, but not Arctic sea ice as whole. The 7,000-year point still stands. Current low ice extent in the Arctic is not `unprecedented', though it is hard to explain given that northern summer sun is weaker than it was 7,000 years ago. I think soot is the more likely answer than air temperatures.